This invention relates to method and apparatus for testing hydraulic releases. It is believed that such apparatus is classified in U.S. Class 73-4 and International Class GOIL 27/100.
Life rafts on large vessels are most often held in place by hydraulic latch devices which are intended to release hydraulically when and if the vessel is submerged. These latches are tested and certified periodically in installations certified by the U.S. Coast Guard and U.S. Navy. Experience has shown that the existing test techniques are inadequate to assure the dependability of the latches. Despite testing failure rates are very high, perhaps approaching 20%. As a consequence, there is a trend for shippers to seek permission to use alternate, and theoretically inferior, raft-release apparatus, e.g. float-free tupe mechanisms.
Because of the theoretical superiority of the hydraulic-release device and the fact that so many shippers are already committed to their use, there is a need to provide a better testing method to assure the performance of these devices.
The most pertinent prior art is disclosed in U.S. Pat. No. 4,018,079. In that patent are shown release devices of the type to which this disclosure relates. Also shown in that patent is a testing procedure generally analogous to the procedure described herein, but over which the procedure described herein is an enormous improvement.
There are a number of kinds of hydraulic release devices presently available. Each of them comprise two separable components one of which includes a hydraulic pressure-actuated device, which upon actuation at the appropriate water depth, normally acts to open a mechanical release thereby separating the two components.
In general, the purpose of the testing is to test the ability of the hydraulically-actuated release mechanism to operate, that is to disconnect the two components, within the desired range of hydraulic pressures. In actual use conditions, this must be accomplished while the device is under stresses caused by buoyancy of the raft and, often, unforseen stresses incident to the sinking of a vessel. Thus it is desirable that a test stress on the overall latch device which simulates those stresses which may be encountered, for one reason or another, just when the device is most needed. For example, as a ship sinks, a latch device may be subjected to a variety of stresses, say from buoyancy effects on a raft, which may interfere with the separation of the aforesaid two components at the desired hydraulic pressure.
In the presently-used release latches, it is possible for these buoyancy or other stress effects to cause sufficient force to be transmitted from at least one of the separable components to the other components or to the hydraulically-actuated mechanism, e.g. a plunger spring of the diaphragm, that the release simply fails to operate at its design pressure even if the hydraulically-actuated mechanism carried by one of the components, is itself in good operating order.
It has been the practice of the prior art to put a given pull on latches during testing which may differ substantially from latch to latch depending on the type of latch that it is.
The inventor has addressed himself to providing a convenient and practical means to test release latches in such a way as to detect the ability of a latch to operate under the stress conditions which simulate those conditions it may encounter in actual use.
The description hereinbelow is described with specific reference to one of the more frequently used latch devices which is set forth for illustrative purposes in FIGS. 4 and 5. FIG. 4 shows the device in latched position wherein pivotally mounted pawls 100 on component 102 are locked onto locking bars 200 on component 202. This locking effect continues until a hydraulically-actuated plunger 204 is depressed beneath the pawls 100 and they are allowed to swing inwardly as seen in FIG. 5, thereby releasing the latch.
The problem arises in that the stresses encountered in actual use can cause undesirable frictional forces between pawls 100 and plunger 104 or even between pawls 100 and locking bars 200. These forces can substantially change the operating characteristics of the latch device.
The latch device of FIGS. 4 and 5 shows a compression spring 80. However, not all devices have compression springs and the problems discussed above exist whether or not compression springs occur in a device. It should be realized that the operation of the testing procedure overides any weakness or other defect in the spring. It is not unusual for the spring to be wholly overidden, i.e. compressed to its maximum compression during illustrated process for preparing a latch for testing. Thus, no assumption is made about the compressive values of the springs during the testing procedure, and the validity of the test procedure is not dependent on the integrity of any such spring which may be present in the particular device to be tested.